Final answer:
The substance that is a nonelectrolyte is CH₃OH.
Step-by-step explanation:
A substance that is a nonelectrolyte does not conduct electricity when dissolved in water, while an electrolyte does. To determine which of the given substances is a nonelectrolyte, we can look at their ability to dissociate into ions in water.
(a) Na₃PO₄: This is an electrolyte because it dissociates into Na⁺ and PO₄³⁻ ions in water.
(b) CH₃OH: This is a nonelectrolyte because it does not dissociate into ions in water.
(c) NH₄Cl: This is an electrolyte because it dissociates into NH₄⁺ and Cl⁻ ions in water.
(d) NaOH: This is an electrolyte because it dissociates into Na⁺ and OH⁻ ions in water.
Therefore, CH₃OH is the substance that is a nonelectrolyte.